1. Field of the Invention
The present invention relates generally to a wind power generation system, and more particularly to a vertical wind power generator with automatically unstretchable blades.
2. Description of the Related Art
Recently, energy saving and environmental protection issues have been more and more emphasized. To cope with greenhouse effect and reduce discharge of carbon dioxide, almost all the countries over the world have positively developed natural resource power generation as substitute and renewable energy sources, including wind power, solar energy, seawater, etc. In these natural resources, the wind power generation technique is the most mature measure and has widest application range. Moreover, the cost for wind power generation is relative low.
A wind power generator operates in such a manner that the blades are driven and rotated by airflow to convert the kinetic energy of the wind into useful mechanical energy or electrical energy. The wind power generators can be divided into horizontal wind power generators and vertical wind power generators according to the relative positions between the shaft of the generator and the horizon. The power generation efficiency of the horizontal wind power generator is higher than that of the vertical wind power generator. However, the rotational faces of the blades of the horizontal wind power generator must face the wind to achieve better power generation efficiency. Therefore, the horizontal wind power generator has more complicated structure and is manufactured at higher cost. The vertical wind power generator has poorer power generation efficiency. However, the rotational shaft of the vertical wind power generator is normal to the horizon. In this case, the blades of the generator can be rotated by the wind in any direction to generate power. Moreover, the vertical wind power generator has the advantages of smaller radius of gyration, simplified structure, low noise and better appearance. Therefore, the vertical wind power generator is more applicable to those sites with limited wind area and rapidly changed wind direction and wind speed, such as the roof of an urban building.
The vertical wind power generators can be divided into lifting type and resistance type according to the working principle of the blades. The lifting type blades are driven and rotated by lifting force and have faster rotational speed as well as better rotational efficiency. On the other hand, the resistance type blades are driven and rotated under the resistance and have larger torque and better actuation ability. These two types of blades have their advantages respectively. Therefore, some modern vertical wind power generators are equipped with both resistance type blades and lifting type blades to achieve the objects of low wind speed actuation and high rotational speed power generation. However, at high rotational speed, the resistance type blades will apply a resistance to the entire wind power generation system against the rotation. This will reduce the rotational efficiency and lower the power generation efficiency.